1. Field of the Invention
The present invention relates to a transmission/coupling device and an image forming apparatus having the same.
2. Description of the Related Art
Japanese Unexamined Patent Publication (Kokai) No. 1-164818 discloses a transmission/coupling device used in a copying machine for coupling a photo-sensitive drum with a drive unit thereof. According to this transmission/coupling device, one member (coupling member) has a conical projection on the rotary axis thereof and a pair of engagement pins projected forward from the peripheral area thereof. On the other hand, another member (coupling member) has a conical recess corresponding to the conical projection on the rotary axis and a pair of engagement ribs provided corresponding to the engagement pins. When the coupling members are coupled with each other on the rotary axis, the projection is pushingly engaged with the recess to locate each of the engagement pins between both the engagement ribs. Thus, two power-transmission points are provided.
According to the technology disclosed in the above Patent Publication, since the projection is fit to the recess to be in surface-contact with each other, a tight coupling can be achieved. However, since the positional or angular offset of the axes of both the members is not allowable in this structure, it is necessary to provide a movable coupling member for the purpose of absorbing such an offset. Also, since this technology solely relates to a torque transmission between axes but not to a uniform velocity transmission, there is a risk of positional offset of printed images or colors. That is, it is actually and practically difficult to completely coincide a rotary axis of a photo-sensitive drum of a replaceable type with an output shaft of a drive motor. If the axial offset is present, even if a regular rotation is input, an irregular rotation (non-uniform velocity) is output under such a circumstance.